At this point, I’m planning to move away from Wordpress due to the instability and into a regular wiki based site. Unsure of which at the moment, maybe some suggestions? Prefer static file based rather than host a DB.
Depends on your target user. If you want something really simple for developers, https://github.com/gollum/gollum is pretty neat (is what powers the Wiki system on GitHub), while if you want something simple for people who aren't developers, something like Mediawiki would fit better. Although Mediawiki requires a database, you can use SQLite (which is basically a file on disk as a DB) for it.
Dokuwiki is also a neat old-school alternative that basically treats files on disk as articles/pages, so no (other) DB needed.
Hugo has been wonderful for me. I use it to host my portfolio website. Only thing I dislike is themes can be a pain to edit if you don’t know where things are spread out in the source.
GravCMS is a flat-file CMS (content is saved to markdown, making it quite portable if you decide it's not for you). There isn't wiki-functionality (auto-create pages that don't exist), however.
Instead of a wiki, why not a static site generator.
I have used Pelican[1] for over a decade. Strongly recommend if you know Python. You don't need to know Python, but in the off chance that one day in the future you want to write your own plugin...
I've been extremely happy with Directs + Astro (and Svelte for some reactive components). It has a weird license where it is open source but they require you to purchase a license if your company goes over $5 million in revenue. But it's such a nice piece of BaaS.
ghost is worse than wp imho. Lots of sneaky affiliate links, and they only integrate stuff that does affiliate linking; the self-hosted version calls home as well.